On the surface of a material made of pure aluminum or an aluminum alloy (collectively hereinafter referred to as “aluminum-based metal”), a dense and strong oxide film is formed, and because its presence poses an obstacle, joining of these aluminum-based metals is difficult in metallurgical processes.
For example, in Japanese Patent Publication of Application, No. JP 3-66072, it is described that, when joining the aluminum materials or joining an aluminum and alumina, by interposing an insert material containing an element causing the eutectic reaction with the base material between the surfaces to be bonded, after being contacted in an oxygen atmosphere and heated to a temperature range in which the eutectic reaction may occur, a phase of melt due to the eutectic reaction and an oxide film phase due to reaction between component in the melt phase and oxygen present in the gap of contact surface between the base component and contact surface occur. Therefore, the oxide film on the surface of the base material is destroyed, and, along with the oxide by the reaction of the oxygen and the melt component, is mixed in the melt phase.
Further, a joining technique for aluminum-based metal, brazing using a brazing material made of Al—Si alloy, is also known. In this case, however, by using the flux of fluoride, for example, oxide film will be removed.
However, in the above mentioned process, the insert material of copper, silver, silicon, aluminum-silver hypereutectic alloy, aluminum-copper hypereutectic alloy, aluminum-silicon hypereutectic alloy is used. Therefore, since the eutectic temperature between these insert materials and aluminum exceeds 500° C. (in the Al—Cu system, 548° C., in the Al—Si system, 577° C., respectively, for example), the junction temperature is high, and especially with heat treatment alloy like 6000 system, even exceeds a solution treatment temperature, the problem arises that the base material is softened and strength is thus lowered. Further, since the joining is performed in an oxygen atmosphere, a special chamber is required with a problem in that the equipment cost increases.